This invention relates to a process of deinking cellulosic materials and in particular to a process of deinking a broad spectrum of printed products including newspaper, laser written paper, xerographic paper, rotogravure, heatset, including coated and uncoated stock and high gloss multi-colored paper, such as magazines.
Conventional methods of deinking and reclaiming waste paper have involved cooking of waste stock in various aqueous deinking chemicals. Such methods were reasonably satisfactory and adequate a number of years ago when there was no need to deink and reclaim waste paper having little or no quantities of ground wood. Such papers were printed with standard inks which are more readily removed or saponified with chemicals at elevated temperatures.
In recent years, however, methods of deinking which involve cooking and the use of chemicals in aqueous media have become increasingly unsatisfactory for a number of reasons. Ink formulations have become more and more complex and involve an increasing use of a wide variety of synthetic resins and plasticizers; with each ink having its own special formulation. Also, increasing amounts of synthetic resins and plasticizers are being used in a wide variety of sizings, coatings, plastic binding adhesives, thermoplastic resins and pressure sensitive label adhesives. Furthermore, the use of multicolored printing and multicolored advertisements have become increasingly popular in recent years and these involve a wide variety of new ink formulations. Many of the new ink formulations incorporate new pigments, dyes and toners which are difficult to remove by conventional aqueous deinking chemicals. The former methods of deinking and reclaiming waste paper by chemical and cooking techniques are not adapted for, or adequate for, removing the new types of inks and coating resins. Due to high contents of thermoplastic resins, the softening action of heat and chemicals alone make their separation from the fibers very difficult. Additionally, the action of heat and chemicals tend to irreversibly set and more firmly bond some of the present day pigments to the fibers and fix dyes and toners to the fibers through staining.
For the above and other reasons, conventional deinking techniques used in reclaiming processes for waste paper are no longer efficient or effective for many current needs.
The need for a satisfactory deinking process has become increasingly important due to greatly expanded utilization of paper and difficulty in disposal of the old papers due to projected lack of landfill sites.
In this regard, to preserve natural resources and minimize environmental problems, the need for developing useful and efficient paper recycling processes becomes of critical importance.
Conventionally, cooking processes for deinking paper have utilized aqueous based suspensions. The stock to be salvaged is first thoroughly cleansed of superficial dirt and then macerated. The maceratum is boiled, subjected to cooking and defiberizing in a suitable aqueous alkali to soften the paper fibers, loosen and disintegrate at least part of the ink and other matter adhering to the fibers, and thoroughly agitated, either while in the alkaline solution or subsequently, to disintegrate and defiber the stock as thoroughly as possible. Thereafter, the pulp is riffled and screened and subsequently dewatered, preferably through suitable rolls, filters, or the like, to remove a considerable portion of the loosened ink. It is then washed and dewatered for removal of additional quantities of the loosened ink as many times as may be practical and expedient.
In general, conventional deinking agents have employed an aqueous alkali solution which may, in addition, contain one or more of the following: a nonionic detergent, a sodium soap of fatty acids or abietic acid sulfonated oil; a dispersing agent to prevent agglomeration of the pigment after release and to emulsify any unsaponifiable material; a softening agent such as kerosine or mineral oil to soften the vehicle of the inks; an agent such as clay, silicate, etc., for selective absorption of pigments after release from the fiber to prevent redeposition on the fiber; and a basic exchange chemical to prevent formation of calcium soaps.
The cooked and defibered pulp is then diluted to less than 1 percent concentration and riffled and screened to remove oversized objects and undefibered pieces of paper. This material is then washed with large amounts of water, an average of 20,000 gallons of water per ton of pulp, to separate the fiber from other substances by washing or screening or by a flotation process. The disposal of large amounts of water used in such processes pose a stream pollution problem which must be remedied.
Another area in which conventional deinking techniques are unsatisfactory in reclaiming waste paper is in the area of electrophotography, better known as xerography. In the art of xerography, an electrostatic xerography latent image is formed by uniformly charging a photoconductive insulating surface of a xerographic plate followed by exposing the charged surface to a pattern of light. The latent image formed by this technique is then developed with an electroscopic powder, also known as a toner, to form a powdered image which is then transferred to a sheet of normal bond paper. The powder image contained on the paper is then fused into the paper to form a permanent reproduction of an original image.
Another means of xerographic development is liquid electrophoretic development, which has particular utility when photoconductive paper is xerographically processed. Developers may be prepared by dispersing finely ground pigments, such as zinc oxide, phthalocyanine blue or nigrosine in an insulating hydrocarbon liquid such as toluene, carbon tetrachloride, or petroleum fractions. The pigment particles acquire electrical charges during dispersion and remain suspended in a liquid. When a photoconductive paper containing an electrostatic image of a polarity opposite to that of the dispersed particles is immersed in the liquid, the pigment particles migrate and become fixed on the latent image.
Laser writing processes also employ various complex dyes and pigments applied to paper by high temperature fusion. These processes are similar, in effect, to the xerographic processes in that ink removal is extremely difficult.
Since ever increasing amounts of xerographic and laser written paper are being used each year, effective processes for reclaiming this type of waste paper are very much needed. However, the effectiveness of any deinking process must take into account the fact that development compositions for xerographic and laser writing processes consist of complicated organic compositions fused under high heat to the paper. With regard to toner development, as heretofore indicated, the toner is usually made of fusible resins or resin blends in which a pigment, such as carbon black has been dispersed. The resins are selected to provide a melting point within the proper range for heat fixing or of a sufficient solubility for solvent vapor fixing. In essence, the action of heat and complex organic chemicals in these printing processes yield printed paper having almost irreversibly stained cellulosic fibers.
In the past, nonaqueous deinking processes have been employed that utilize various chemical additives such as surfactants. U.S. Pat. No. 3,072,521, for example, relates to a nonaqueous process of deinking cellulosic materials employing a surfactant-containing organic solvent. The surfactant is necessary to enable removal of ink from the paper.
Other deinking processes that have been developed utilize partial nonaqueous or immiscible solvents. U.S. Pat. No. 3,635,789, describes a deinking process whereby an immiscible solvent is added to an aqueous pulp suspension to facilitate the removal of ink from the pulp. U.S. Pat. No. 3,891,497, relates to a process for recovering of waste paper using steam and immiscible fluids and a small amount of water. The water is added to the waste paper to make it easier to break the bonds between the fibers. The process is conducted in a pulper at an elevated pressure because high temperatures are employed.